Photo credit: Thomas Gomersall

Starfish Bay Biodiversity

by Thomas Gomersall

Though not the most attractive habitats, the intertidal estuaries of Hong Kong support a vast array of life, including countless snails, worms, crabs and bivalves, such as clams as mussels. So for anyone who enjoys looking for small marine creatures in rock pools or in the sand, estuaries are a treasure trove.

One of the most accessible of these habitats is in Starfish Bay, which is located within easy walking distance of Ma On Shan and, at low tide, is a great place to find some of Hong Kong’s weirdest but most wonderful species. However, it is important to remember that mudflats are fragile habitats that are sensitive to disturbance, particularly to activities like clam digging. So when visiting them, be sure to not disturb wildlife and to avoid walking in sensitive habitats such as mangroves.

Photo credit: Thomas Gomersall

Starfish (Archaster typicus): Found in areas with good water quality and sandy substrates, starfish are not always easy to find as they usually tend to bury themselves in the sand. They have incredible powers of regeneration, being able to grow back a limb if they lose it and even grow extra limbs. From June to August, pairs of starfish may be spotted in their mating pose, with the male lying directly on top of the female with their arms interlocking (Fong et al, 2005, p. 66).

Photo credit: Wong Ho Man

Mud Whelk (Nassarius festivus): Though this sea snail may not be much to look at, it does stand out from most others of its kind in one, slightly gruesome way: it is a meat eater. It scavenges dead fish and bivalves, which it detects using special chemoreceptors that help it to find rotting flesh from a distance (Fong et al, 2005, p. 38). As local villagers frequently dig for clams in estuaries at low tide and discard ones that they don’t want, mud whelks often find plenty to eat and a 2004 study found that the ones in Starfish Bay were the biggest in Hong Kong, thanks to this extra food (Morton & Chan, 2004).

Photo credit: Cynthia Yau

Soldier Crab (Mictyris longicarpus): Resembling a pale-blue marble with legs and pincers, this tiny crab often gathers in large colonies at low tide. They are master diggers; rotating their bodies 360 degrees downwards into the sand, they can very quickly submerge themselves completely. Unlike most crabs, which can only walk sideways, soldier crabs can walk forwards (Fong et al, 2005, p. 51).

Photo credit: Billy Hau

Sea Hibiscus (Hibiscus tiliaceus): This small tree is a common plant along tropical coastlines and is well-adapted to the challenging conditions of these environments. It is able to withstand a range of soil conditions, being able to grow around the mouths of streams and in saltier substrates like those around mangrove forests. Its wood is durable in salt water (so much so that it has even been used to make canoe outriggers) and its seeds are water-dispersed and have special capsules to help them cope with long journeys at sea. (Allen, 2003). It produces large yellow flowers with purple stamens in July and August (Ngar et al, 2007, p. 111).

Photo credit: Thomas Gomersall

White-breasted Waterhen (Amaurornis phoenicurus): The white-breasted waterhen is one of Hong Kong’s most common, adaptable and beautiful resident birds and can be found wherever there is shallow water. One sign of its presence is its harsh, croaking call of ‘kee-wak kee-wak’. Unlike most members of the rail family, it is not a particularly shy bird (Viney et al, 2005, p. 82) and can frequently be seen dashing across the road or foraging near the side of it.

References

· Allen, J.A. 2003. Hibiscus tiliaceus L. Tropical Tree Seed Manual. Reforestation, Nurseries and Genetics Resources.

· Fong, T.C.W, Lai V.C.S and H.T.H. Lui. 2005. Photographic Guide Series of Hong Kong Nature (2): Estuarine Organisms — Mangrove, Mudflat and Seagrass Bed. Jan KC Chan, HK Discovery Limited, Hong Kong. 38pp., 51pp., 66pp.

· Morton, B. and Chan, K. 2004. The population dynamics of Nassarius festivus (Gastropoda: Nassariidae) on three environmentally different beaches in Hong Kong. Journal of Molluscan Studies, vol. 70 (4): 329pp–339pp.

· Ngar, Y.N., Hung, L.C., Chan, S.K. and O.K. Chan. 2007. Hong Kong Wild Flowers, vol. 1, Friends of the Country Parks, Hong Kong. 111pp.

· Viney, C., Phillipps, K. and C.Y. Lam. 2005. The Birds of Hong Kong and South China. Information Services Department, Hong Kong SAR Government, Hong Kong. 82pp.

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WWF contributors share regular insights on Hong Kong biodiversity and conservation issues